1. Field of the Invention
The invention relates to an ink jet recording head in which ink of pressure generating chambers supplied with ink from a reservoir connected to an external ink tank is pressurized by piezoelectric vibrators or heating means and ink droplets are ejected from nozzle openings to form an ink image on a recording sheet.
2. Description of the Related Art
An ink jet recording head basically comprises: a reservoir connected to an external ink tank; a plurality of pressure generating chambers connected to the reservoir via an ink supply port; pressure generating means for pressurizing the pressure generating chambers, such as piezoelectric vibrators or heating means; and nozzle openings from which ink pressurized in the pressure generating chambers is ejected as droplets.
In such an ink jet recording head, as well known in the art, although ink which is pressurized in the pressure generating chambers is mainly ejected as droplets, part of the ink reversely flows to the reservoir for supplying the ink to the pressure generating chambers, via the ink supply port.
When the print density is suddenly changed and the ink consumption is largely varied, therefore, pressure vibration occurs in the reservoir which supplies the ink to the pressure generating chambers. This pressure vibration of the reservoir propagates to all the pressure generating chambers connected to the reservoir, so that also the pressure of the pressure generating chambers is varied, thereby affecting the ejection characteristics. In an extreme case, a crosstalk in which ink droplets are ejected irrespective of a print signal occurs.
This problem is easily produced particularly in an ink jet recording head which has 64 or more nozzle openings and which can be driven at a density of 180 dpi or more and a frequency of 20 kHz or higher.
In order to solve the problem, an ink jet recording head in which a plate wherein nozzle openings are opened, a member for forming a reservoir, and a plate member for forming pressure generating chambers are stacked is proposed in a Japanese patent publication (Kokai) No. HEI9-187932. In the proposed ink jet recording head, a recess which opens toward the pressure generating chambers is formed at a position opposed to the reservoir, to build a thin portion between the plate member for forming the reservoir, and the plate member for forming the pressure generating chambers. A part of the reservoir is absorbed by elastic deformation of the thin portion due to the pressure of ink which reversely flows from the pressure generating chambers.
According to this configuration, the pressure variation due to the ink which reversely flows from the pressure generating chambers can be absorbed as much as possible, and a crosstalk and the like can be prevented from occurring. However, the thin portion must be formed in the plate member. This produces problems such as that the structure and the production steps are complicated, and that it is difficult to provide sufficient compliance.
The invention has been conducted in view of these problems.